The present invention relates to a tone type recognition method and, more particularly, to a method that can recognize a call progress state of a central office line (hereinafter referred to as C.O.L.) switching system by using a tone detector.
The function of recognizing the call progress state of the C.O.L. switching system in various communication devices (PBX, facsimile, modem etc.) that are linked with C.O.L. is important in such aspects of effectively using communication lines and serving subscribers.
To achieve the above object, in a conventional method, relatively expensive integrated circuit chips are employed that recognize respective frequencies by way of hardware manipulating a characteristic that representative call progress tones differ in frequency by their tone types. Accordingly, the prior method is accompanied with a cost-rise factor and has such a disadvantage in that tones with the same frequencies (for example, busy tone and reorder tone) are impossible to distinguish.